It seems to be a problem that often occurs with onePlus3. There are threads on the web that describe the problem and ways to fix it, but it does not work. I've tried everything from updating the OS and drivers and all options in developer option, as described above, unsuccessfully. My conclusion is that there is a hardware problem with the usb plug on the phone. If someone else has a different conclusion, please help us.

Please confirm you have selected "USB Storage" or "File Trasnfer" in USB mode prompt when you connect phone to laptop. If you haven't, i am not sure which cave you were living in but that's how Android's been working from some recent versions.